The present invention relates generally to gas turbine engines, and, more specifically, to combustors therein.
In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases that flow downstream through turbine stages which extract energy therefrom. A high pressure turbine follows the combustor and extracts energy for powering the compressor. And, a low pressure turbine follows the high pressure turbine and extracts additional energy for powering an external load, such as an electrical generator in an exemplary embodiment.
Large industrial power generation gas turbine engines typically include a can combustor having a row of individual combustor cans in which combustion gases are separately generated and collectively discharged into a common high pressure turbine nozzle for redirection into the first stage of turbine rotor blades. Each combustor can is generally cylindrical and has an aft transition section or piece configured for changing the flowpath from circular to a corresponding arcuate portion of an annulus. In this way, the row of cans have corresponding arcuate outlets adjoining each other circumferentially at a common plane defining a segmented annulus for discharging the combustion gases into the common turbine nozzle.
Each combustor can has a corresponding combustor liner in which the combustion gases are bound, with an upstream dome end of the liner having several premixers in which fuel is injected and mixed with air for forming fuel and air mixtures which undergo combustion. Each can generates a corresponding combustion gas stream independently from the other cans, with the several streams being collectively discharged into the common turbine nozzle.
A significant design objective in combustor performance is the dynamic operation thereof. The combustion gases have a corresponding static pressure in each can, and a dynamic pressure response associated with different dynamic modes of response. Combustors are typically designed for minimizing undesirable resonant dynamic response which could lead to fatigue damage in the combustors and adversely affect combustor performance.
Since the can combustors are independent and discrete components, each generating its respective combustion gas stream, the static and dynamic operation of the cans are inter-related at the outlet ends of the combustors and the inlet end of the common turbine nozzle.
Typically, the leading edges of the turbine nozzle vanes are spaced aft from the outlet ends of the combustor cans to provide a common annulus in which the several gas streams are initially discharged into the nozzle. In this way, any differences in static pressure from can to can may be reduced or eliminated by the common annulus for improving performance of the engine.
However, the common annulus provides a mechanism for dynamic interaction between the adjoining cans which may lead to undesirable modal resonance. More specifically, two distinctive types of combustion dynamic modes are known in can combustors. In a push-pull mode of dynamic response, the dynamic pressure in adjoining cans may be out-of-phase; and in a push-push mode of dynamic response, dynamic pressures may have the same phase. These dynamic modes occur at a specific frequency, with resonant modes having elevated dynamic pressure amplitudes, and non-resonant modes having little or no pressure amplitudes or affect.
In general, push-pull modes of dynamic response generate higher pressure amplitudes, and therefore may lead to fatigue damage and adverse performance of the combustor. Correspondingly, push-push modes of dynamic response have little interaction between the cans and do not promote fatigue damage or adversely affect combustor performance.
Accordingly, it is desired to provide an improved can combustor in which push-pull modes of dynamic response are reduced or eliminated for improving combustor performance and correspondingly reducing fatigue damage.